Why don't door hinges wear out from repeated opening and closing?

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oneamp
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The door hinges inside my place are pretty old; I'd guess a few decades though I don't have any way of knowing for sure. I do have experience with metal on metal rubbing and degradation. So I wonder, why can door hinges open and close for a long time, and not wear away? I don't think I've ever seen a door hinge that was worn. It seems like just a little bit of wear would result in the door not opening as smoothly as it should.
 
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What direction is the force applied? think gravity then add the torque for when the door is opened. The wear will be top down, with slight spreading depending on the hinge style on a pin hinge the wear is usually on the pin. Just makes the hinge looser.
 
But doors do not open in a way that evenly wears the entire hinge surface. So a pit should develop.
 
The hinge pin has a small diameter so the friction surface velocity is very low. The contact surfaces remain covered so abrasive dust is unlikely to enter. The hinge is usually operated rarely, and slowly, over less than 90°.

The hinge pin needs to support someone occasionally swinging on the door. It is therefore more robust than is needed just to support the door.
 
And some people may oil door hinges so you don't get that creaaaaaaking sound like in a horror movie.